A known technique for transmitting multiple signal components as a single optical signal is known as wavelength division multiplexing (WDM). In a WDM signal, each signal component has a respective different frequency or wavelength. Each frequency or wavelength is sometimes referred to as a channel. Various devices have been developed to optically separate or combine the signal components, including multiplexers, demultiplexers and optical add/drop modules. There is a progressively growing demand in the market for devices of this type which have a high channel count, or in other words which can handle optical signals with a large number of signal components at respective different frequencies. Currently, there is a growing demand for devices capable of handling optical signals with 16 to 80 signal components, or an even greater number of signal components. There is also a demand for these devices to have a low insertion loss, and to be packaged in a compact manner.
In attempt to meet this demand, devices have been developed which utilize a dispersive element to facilitate optical separation or combination of multiple signal components. In order to reliably achieve satisfactory performance, these devices are manufactured according to extremely tight tolerances for a number of different physical and optical characteristics. An example of one such device is a demultiplexer which has the end of an input fiber and the ends of several output fibers secured at predetermined locations on a support member, and which has optical and dispersive components disposed on the support member between the input and output fibers so that each signal component of a WDM signal arriving through the input fiber is focused on the end of a respective output fiber. In this device, the support member and the optical and dispersive components are all fabricated according to extremely strict tolerences to ensure that, when the device is put into production, each signal component will be fairly accurately focused onto the end of a respective output fiber in each production device.
While pre-existing devices of this type have been generally adequate for their intended purposes, they have not been satisfactory in all respects. For example, the need for extremely tight tolerances as to a large number of physical and optical characteristics causes these devices to have a number of components which are each very expensive to manufacture. As a result, the device itself is undesirably expensive. Moreover, despite the use of tight tolerances, not every signal component ends up being accurately focused on the end of the corresponding output fiber. Consequently, characteristics like insertion loss are not always optimum, and may vary from system to system, for example where a given subset of tolerance variations offset each other in one system, but are cumulative in another system.